Summary
This controlled crossover study examined whether increasing dietary polyunsaturated fat (PUFA) affects oxidative stress in humans. Ten healthy men consumed two four-week diets—one low in PUFA (5% of calories) and one high in PUFA (15%)—with identical total fat, carbohydrate, protein, and vitamin E content. The high-PUFA diet led to increased oxidative stress, shown by higher oxidized glutathione in whole blood and elevated urinary TBARS, while these markers decreased on the low-PUFA diet. Most plasma oxidation markers and several red-blood-cell antioxidant enzymes did not change, though superoxide dismutase was lower during the low-PUFA phase. Additionally, total cholesterol rose by 13% on the low-PUFA diet, aligning with PUFA’s known cholesterol-lowering effects. Overall, the findings highlight a trade-off: higher PUFA intake can improve cholesterol levels but may also raise oxidative stress, suggesting that recommendations to increase PUFA should consider concurrent antioxidant support to protect these oxidation-prone fats.
PMID: 10452406
DOI: 10.1038/sj.ejcn.1600783
Abstract
Objective: To assess whether nutritionally-relevant changes in polyunsaturated fatty acid (PUFA) intake alter indices of oxidative stress in human volunteers
Design: A split plot/change over dietary study where half the volunteers consumed a diet containing 5% PUFA (low PUFA) as food energy for 4 weeks and after a 6 week washout period consumed a 15% PUFA (high PUFA) diet for another 4 weeks. The second group of volunteers completed this protocol in reverse. Total fat, carbohydrate, protein and vitamin E contents of the diets were constant.
Subjects: 10 healthy, non-smoking, male volunteers aged 32.6±1.7 y
Results: There was a significant increase in whole blood oxidised glutathione (P<0.05), an index of oxidative stress, after consumption of the high PUFA diet. Moreover, urinary thiobarbituric acid reactive substances (TBARS), an index of lipid peroxidation, significantly increased (P=0.038) following consumption of the high PUFA diet and decreased (P=0.031) after consuming the low PUFA diet. However, there was no change in non specific plasma indices of lipid peroxidation, conjugated dienes and TBARS, nor in red cell antioxidant enzymes glutathione peroxidase, glutathione reductase, and catalase. However, superoxide dismutase significantly decreased (13%, P=0.018) after consumption of the low PUFA diet. Total cholesterol increased by 13% (P=0.014) after consumption of the low PUFA diet.
Conclusions: This study indicates that although increasing dietary levels of PUFA may favourably alter cholesterol profiles, the same dietary changes may adversely affect some indices of lipid peroxidation. Care should be taken when providing dietary advice on PUFA intake and an adequate intake of antioxidants to match any increased PUFA may be important for preventing oxidative stress.
Sponsorship: Ministry of Agriculture, Fisheries and Food (MAFF) and the Scottish Office Agriculture, Environment, and Fisheries Department (SOAEFD)
Jenkinson A, Franklin MF, Wahle K, Duthie GG. Dietary intakes of polyunsaturated fatty acids and indices of oxidative stress in human volunteers. Eur J Clin Nutr. 1999 Jul;53(7):523-8. doi: 10.1038/sj.ejcn.1600783. PMID: 10452406.